Iron deficiency is currently one of the most prevalent nutritional deficiency problems in the world. A number of studies have demonstrated that people with iron deficiency have depressed immune function, limitations in cognitive functioning and poor work performance. The specific aim of this study is to test the effects of iron deficiency on the cognitive performance of young women (18-35) and to test if alterations in cognitive performance are reversible following the repletion of iron stores. This study will test the hypothesis that iron deficiency in young women will result in alterations in cognitive performance and that these alterations are reversible as a result of iron repletion. All subjects will perform cognitive tests on a computer as well as paper/pencil tasks, complete 2 day dietary food records and have blood drawn. The iron deficient subjects will then be supplemented for 4 months while the iron suffcient subjects (control) will receive a placebo. All testing will be repeated after the 4 month intervention.